Pillared micas

ABSTRACT

This invention relates to pillared micas, which comprise an active metal selected from the group consisting of Pt, Cr, Pd, It, Rh and mixtures thereof, and a first modifier metal selected from the group consisting of Sn, Ga and mixtures thereof. The mica may also be modified with a second modifier metal selected from the group consisting of alkali metals, alkaline earth metals, or rare earth metals and mixtures thereof. This invention further relates to a process for preparing such a catalyst.

FIELD OF THE INVENTION

This invention relates to pillared micas which contain an active metal selected from the group consisting of Pt, Cr and mixtures thereof, and a first modifier metal selected from the group consisting of Sn, Ga and mixtures thereof. The micas may also contain a second modifier metal selected from the group consisting of alkali metals, alkaline earth metals, and rare earth metals, and mixtures thereof. This invention further relates to a process for preparing such pillared micas.

BACKGROUND OF THE INVENTION

Micas are composed of layers. Each mica layer may be visualized as a sandwich comprising two outer layers of silicon tetrahedra and an inner layer of aluminum octahedra (i.e., 2:1 layered mica). These micas are generally represented by the general formula:

    A.sub.x [M.sub.2-3 T.sub.4 O.sub.10 (OH).sub.2 ]

where M designates the octahedral cation, T designates the tetrahedral cation, and A designates the exchangeable interlayer cations. The T coordinated ion is commonly Si⁺⁴, Al⁺³, or Fe⁺³, but could also include several other four-coordinate ions, e.g., P⁺⁵, B⁺³, Ga⁺³, Cr⁺³, Ge⁺⁴, Be⁺², etc. The M coordinated ion is typically Al⁺³ or Mg⁺², but could also include many other possible hexacoordinate ions, e.g., Fe⁺³, Fe⁺², Ni⁺², Co⁺², Li⁺, Cr⁺³, V⁺³, etc. Mg⁺² is preferred in this invention.

The preparation of pillared tetrasilicic micas for use as catalyst supports is disclosed in a paper by J. W. Johnson and John F. Brody, "Pillared Clays and Micas," Materials Research Society Symposium Proceedings 111, 257 (1988). A method of catalytic cracking, isomerizing or reforming hydrocarbons employing pillared fluorotetrasilicic micas is disclosed in European patent Application No. 0341023A2. The preparation of transition-metal pillared micas which are prepared from transition metal-pillaring solutions is described in U.S. Pat. No. 4,666,877. Uses of Pt-pillared clays, or micas, are described in V. N. Parulekar and J. W. Hightower, "Hydroisomerization of n-Paraffins on a Platinum-Rhenium/Pillared Clay Mineral catalyst," Applied Catalysis 35, 249-262 (1987) and C. Doblin, J. F. Mathews, and T. W. Turney, "Hydrocracking and Isomerization of n-Octane and 2,2,4-Trimethylpentane over a Pt/Alumina-Pillared Clay," Applied Catalysis 70, 197-212 (1991). Consequently, while micas and clays are taught as being a suitable catalyst support for a variety of petrochemical reactions, pillared micas are not taught as being useful for dehydrogenation catalysts.

Transportation fuels, particularly motor gasoline, contains a relatively high level of aromatic components, such as benzene. These fuels, while relative high in octane number, are facing ever growing difficulty meeting ever stricter governmental environmental regulations with regard to emissions. This is primarily because of the high levels of aromatics. Consequently, there is much work being done to develop what has become known as "low emissions fuels". An important aspect of this work involves the substitution of non-aromatic components, having a relatively high octane value, for aromatic components of the fuel.

A class of non-aromatic components having relatively high octane value, which has been proposed for the production of low emissions fuels, are oxygenates. Non-limiting examples of preferred oxygenates for use in low emissions fuels include the unsymmetrical dialkyl ethers, particularly methyl tert-butyl ether (MTBE), ethyl tert-butyl ether (ETBE), and tert-amylmethyl ether (TAME). Conventional methods of manufacture of such ethers are typically based on liquid-phase reactions, such as the reaction of iso-butylene with methanol over cation-exchanged resins. This has created substantial demand for oxygenate building blocks, such as iso-butylene. Furthermore, other low carbon, or light, olefins are also in demand for the same reasons.

Low carbon number olefins, for example those having 2 to 10 carbon atoms, are typically obtained by the dehydrogenation of the corresponding paraffinic hydrocarbon. One method for light paraffin dehydrogenation is the so-called oxidative dehydrogenation process. In this process the light alkanes are reacted with oxygen over a suitably prepared mixed metal oxide catalyst to produce a mixture of olefin, water, CO_(x), and unreacted paraffin. While high conversions combined with high olefin selectivities can be achieved, such a process has a number of disadvantages including loss of fuel value due to water and CO_(x) formation. Furthermore, process operations are relatively costly and there are industrial hazards associated with exothermic combustion reactions.

A more direct and preferred approach is direct dehydrogenation over a suitable catalyst to produce olefins and molecular hydrogen. This chemistry has recently received considerable interest, although high reaction temperatures in the range of 500°-650° C. are required to obtain a significant equilibrium yield (e.g., 15-65%) of olefin. Moreover, under these reaction conditions, light alkane hydrogenolysis, for example to methane, is a competing and undesirable reaction. Most catalysts studied to date have not shown very high selectivities for dehydrogenation versus hydrogenolysis, or they have suffered from rapid catalyst deactivation necessitating frequent regeneration. As a consequence, process economics have not been favorable. Consequently, incentives exist for catalysts which: have high selectivity for the production of olefins; have improved resistance to deactivation; and can be regenerated using simple procedures, such as air treatment.

SUMMARY OF THE INVENTION

The instant invention is a pillared mica comprising an active metal selected from the group consisting of Pt, Cr, Pd, It, Rh and mixtures thereof, and a first modifier metal selected from the group consisting of Sn, Ga and mixtures thereof. The mica may be further modified with a metal selected from the group consisting of alkali metals (e.g., Na), alkaline earth metals (e.g., Mg, Ca), and rare earth elements (e.g., Nd, La, Ce) and mixtures thereof.

In a preferred embodiment of the present invention, about 0.05 to 2 wt. % of active metal is present. Furthermore, from about 0.05 to 5 wt. % of at least one first modifier metal selected from Sn and Ga is incorporated. Up to 4 wt. % of at least one second modifier metal selected from the alkali, alkaline earth and rare earth metals may additionally be present.

The present invention also relates to a process for preparing the above-mentioned mica, which comprises:

(a) treating a mica with an aqueous polymeric cationic hydroxy multimetal complex solution comprising: (i) a polymeric cationic hydroxy complex solution, wherein the cation is selected from the group consisting of aluminum, zirconium, chromium and mixtures thereof, and (ii) an active metal compound wherein the metal is selected from the group consisting of Pt, Cr, Pd, It, Rh and mixtures thereof;

(b) calcining said treated mica for an effective amount of time at an effective temperature, thereby forming metal oxide pillars between the mica layers; and

(c) incorporating from about 0.05 to 5 wt. % of a first modifier metal selected from the group consisting of Sn, Ga and mixtures thereof.

In a preferred embodiment, the pillared mica contains from 0.1 to 4 wt. % of a second modifier metal selected from the group consisting of alkali, alkaline earth, and rare earth metals, and mixtures thereof.

DETAILED DESCRIPTION OF INVENTION

Hydrocarbon streams which can be dehydrogenated using the pillared micas of the present invention are those streams containing predominantly C₂ to C₁₀ hydrocarbons. The preferred C₂ to C₁₀ hydrocarbons are alkanes; alkenes; alicyclic compounds, such as cyclohexane; alkylaryl compounds, wherein the alkyl group contains from about 2 to 10 carbon atoms, such as ethylbenzene; and naphthenoaromatics, such as tetrahydronaphthalene. Particularly preferred are C₂ to C₆ hydrocarbons, and more particularly preferred are C₂ to C₅ hydrocarbons, especially the alkanes, iso-butane and isopentane. It is to be understood that derivatives of the above hydrocarbons may also be used in the practice of the present invention, such as alcohols, halides, carboxylic acids, and the like. Typical hydrocarbon streams which will be treated in accordance with the present invention are petroleum refinery streams. Non-limiting examples of such streams are the C₂ to C₆ streams which result from reforming, coking, hydrocracking, distillation, and fluid catalytic cracking.

The catalyst of the present invention can be prepared from synthetic fluoromicas such as sodium tetrasilicic mica (NaTSM) and synthetic taenionlite. Tetrasilicic micas may, in this application, also be described as tetrasilicic fluoromicas. Synthetic fluoromicas, such as sodium tetrasilicic mica (Na[Mg₂.5 Si₄ O₁₀ F₂ ]), and lithium taeniolite (Li[(Mg₂ Li)Si₄ O₁₀ F₂ ]) undergo swelling in water and other suitable polar solvents which enables the micas to be pillared. Even though fluoromicas such as these exhibit high layer charge densities they are capable of undergoing pillaring reactions with large cations. The resulting pillared tetrasilicic micas exhibit good thermal stability and are typically good catalysts for cracking, isomerization, etc.

The pillared micas of the present invention possess an internal microstructure which may be established by introducing discrete, non-continuous inorganic oxide particles, or pillars, having a height between about 5 and 20Å, preferably 6 to 18 Å, more preferably 6 to16 Å, between the mica layers. The primary layers in 2:1 clay minerals are about 10 Åthick. Much work has been done to demonstrate that these platelets may be separated further by insertion of various polar molecules, such as water, ethylene glycol, various amines, etc., and that the platelets can be separated by as much as 30 to 40 Å. In the present invention, the pillars are preferably composed of alumina (Al₂ O₃). These pillars serve to hold the space between the clay layers open after removal of occluded water and serve to form an internal interconnected micropore structure throughout the inner layer in which the majority of the pores are less than about 30 Å in diameter.

The micas of the present invention may be produced by reacting the synthetic fluoromica with a polymeric cationic hydroxy multimetal complex. This complex may itself be produced by reacting a solution containing certain active metal-containing compounds with a polymeric cationic hydroxy complex solution. Preferred active metals are Pt, Pd, Cr, It, and Rh. More preferred is Pt, particularly the form of dihydrogen hexachloroplatinum. The cation of the complex is selected from aluminum, zirconium, and chromium. A preferred polymeric cationic hydroxy complex solution is an aluminum chlorohydroxide solution, such as "CHLORHYDROL MICRO-DRY", manufactured by Reheis Chemical Co. and containing about 23.5 wt. % Al₂ O₃. Also suitable are any partially hydrolyzed alumina solutions containing aluminum polyoxocations. The solution may be heated to convert the hydrolyzed polymer complex into a polymeric cationic hydroxy multimetal complex. The polymeric cationic hydroxy multimetal complex may be, of course, produced by a variety of other ways, including introducing additional metals as modifiers into the initial cationic solutions used in the polymer synthesis. Such additional modifier metals may include a first modifier selected from Sn and Ga, and optionally a second modifier metal selected from the alkali, alkaline-earth, and rare earth metals.

In one embodiment of the present invention, the modified pillared micas incorporate an effective amount of a second modifier metal selected from alkali, alkaline earth, rare earth metals and mixtures thereof, in addition to the active metal and the first modifier metal. By the term "effective amount of modifier" is meant that concentration range of modifier which will improve the selectivity and reduce the cracking tendencies of the resulting micas when used for the dehydrogenation of C₂ to C₁₀, preferably C₂ to C₅, hydrocarbons. Suitable examples of modifiers include alkali metals such as Na and Li, preferably Na; alkaline earth metals such as Mg and Ca, preferably Mg; and rare earth metals such as Nd, La, Ce.

The active metal component, or mixtures thereof, may be present in the range of from about 0.05 to 2 wt. %, preferably 0.1 to 1.5 wt. % and more preferably from 0.15 to 1 wt. %. If both Sn and Ga are present as a first modifier metal, then the combined amount may be from about 0.05 to 5 wt. %. If Sn is present alone, the preferred amount is from about 0.1 to 1 wt. % and the most preferred amount is from about 0.15 to about 0.8 wt. %. If Ga is present alone, the preferred amount is from about 0.1 to 3 wt. % and the most preferred amount is from about 0.15 to about 2.5 wt. %. If a second modifier metal is used, the amount will range from about 0.1 to 2 wt. %, preferably from about 0.1 to 1 wt. %, and most preferably from about 0.2 to 0.6 wt. %. This is in addition to any native alkali or alkaline earth metals present in the unwashed mica.

Both the first and second modifier metals may be incorporated into the pillared micas by techniques such as by impregnation on the pillars prior to pilling and crushing of the finished catalyst. If impregnation is used, the pillared mica, in a dry or solvated state, is contacted, or otherwise incorporated with, a solution containing one or more of the modifier metals and thereby impregnated by the "incipient wetness" technique. Separate solutions can be used to incorporate each metal, or more than one metal can be incorporated with a single solution. This technique embodies absorption from a dilute or concentrated aqueous solution, with the total uptake of the metallic components being effected by filtration or evaporation. The solution used in impregnation can be a salt or acid solution having the respective modifier metal. Gallium nitrate is a convenient precursor for pillared mica modification, although other water and organic soluble compounds of Sn, Ga, or alkali, alkaline-earth, or rare earth metals may also be used. The impregnation treatment can be carried out under a wide range of conditions, including ambient as well as elevated temperatures. Atmospheric or superatmospheric pressures may be used. Such techniques are within the skill of those of the art and a more detailed description of such "incipient wetness" techniques is not necessary herein.

The conditions below represent general dehydrogenation conditions suitable for use with the micas of the present invention.

    ______________________________________                                         Major Operating                                                                             Typical Process                                                                            Preferred Process                                     Variables    Conditions  Conditions                                            ______________________________________                                         Pressure, psia                                                                              >0-50        1-20                                                 Reactor Temp., °C.                                                                   400-650     500-625                                               H.sub.2 /Alkane                                                                             0-5         0-3                                                   Molar Feed Ratio                                                               Feed Rate, LHSV*                                                                            0.5-7       1-3                                                   ______________________________________                                          *(liquid hourly space velocity = volume of liquid per volume of catalyst       per hour)                                                                

The following examples are presented for illustrative purposes and are not to be taken as limiting in any way.

EXAMPLES

The pillared micas of the instant invention were prepared by the following procedure:

500 grams of tetrasilicic mica, designated as NA-T5 (DM Clean A) obtained from Showa Sangyo Co., Ltd., were dispersed in 20 liters of deionized water by mixing 5 batches of 100 grams of said mica in 4 liters of water and blending each batch for 4 minutes. Each batch of blended mica mix was then decanted into a glass reaction vessel. The pH of the mica mix was adjusted to 5.0 as it was stirred. The mixture was allowed to settle for 1 hour. The mica mix was then spray-dried at an inlet temperature of 230°-250° C., an outlet temperature of 120°-135° C. and a feed rate of 4-5 liters/hour.

152.5 grams of CHLORHYDROL MICRO-DRY aluminum chlorohydrate powder, which contains 47.2 wt. % Al₂ O₃, was mixed into 125 grams of deionized water in a reaction flask fitted with a condenser. Dihydrogen hexachloro-platinum (e.g. 0.6 wt. % Pt) and/or alkali (e.g. sodium nitrate), alkaline earth (e.g. magnesium nitrate), rare earth (e.g. neodymium nitrate) salts were added to the CHLORHYDROL solution. The Pt- and/or Pt-alkali-, Pt-alkaline-, Pt-rare earth-CHLORHYDROL solutions were heated to 90° C. with stirring for 24 hours and cooled to room temperature (about 22° C.). 4.5 liters of deionized water was added to the cooled solutions with stirring. Stirring was continued for 1 hour. The solution was then allowed to stand overnight at room temperature, thereby forming a polymeric cationic hydroxy multimetal complex. The composition of the complex used in any given example herein is indicated in the tables to follow.

225.8 grams of the spray-dried mica were added to the Pt-and/or Pt-alkali-, Pt-alkaline earth-, Pt-rare earth-CHLORHYDROL solutions with stirring and were heated to 90° C. Heating continued overnight. The dispersion was cooled and filtered. The filter cake was dispersed in 25.0 liters deionized water and filtered. This process was repeated until the filtrate was substantially chloride-free. The filter cake was dried at 127° C. overnight. It was calcined in air for 2 hours at 200° C., heated to 400° C. at 50° C./minute and held at 400° C. for 2 hours. The calcined material was washed by dispersion in 50.0 liters deionized water and filtered. The wash was repeated twice reducing sodium levels to about 0.4% by weight. The material was dried overnight at 127° C. The calcination step was repeated. In a more preferred embodiment, the washing step was omitted and sodium levels were maintained at from about 1.2 to 1.4% by weight. SnCl₂ (e.g. 0.4 wt. % Sn) or Ga(NO₃)₃ (e.g. 2.5 wt. % Ga) was added to the Pt-, Pt-alkali-, Pt-alkaline, Pt-rare earth-aluminum tetrasilicic mica via incipient wetness techniques and dried at 100° C. overnight. The micas were pilled and crushed as 14/35 mesh particles. The surface area measured by the nitrogen BET method ranges from 220 to 340 m² /g, and the layer repeat distance measured by X-ray powder diffraction was 18.2 to 18.8 Å.

The comparative clays were prepared by the following procedure:

277.5 grams of CHLORHYDROL 50% aluminum chlorohydrate solution (containing about 23.5% Al₂ O₃, manufactured by Reheis Chemical Co.), was added to a reaction flask fitted with a condenser. This solution was then heated to 90° C. with stirring for 24 hours and was then allowed to cool to room temperature. 10.880 grams of AESAR dihydrogen hexachloroplatinum (IV) was then added. 4.5 liters of deionized water was added to the cool solutions with stirring. Stirring was continued for 2 hours. The solution was then allowed to stand overnight at room temperature, thereby forming a polymeric cationic hydroxy multimetal complex.

370.5 grams of VOLCLAY HPM-20, a technical grade microfine sodium bentonite clay obtained from the American Colloid Co., was added to the Pt-CHLORHYDROL solution with stirring and was heated to 90° C. Heating continued overnight. The resulting dispersion was cooled and filtered again. The filter cake was dispersed in 25.0 liters deionized water and filtered again. This process was repeated until the filtrate was substantially chloride-free. The filter cake was dried at 127° C. overnight. It was calcined in air for 2 hours at 200° C., heated at 400° C. at 50° C./minute and held for 2 hours. The calcined material was washed by dispersion in 50.0 liters deionized water and filtered. The wash was repeated twice. The calcined material was dried overnight at 127° C. The calcination step was repeated. SnCl₂ (e.g. 0.4 wt. % Sn) or Ga (NO₃)₃ (e.g. 2.5 wt. % Ga) was added to the Pt-, Pt-aluminum bentonite via incipient wetness techniques and dried at 100° C. overnight. The resulting clay micas were pilled and crushed as 14/35 mesh particles. They have a surface area of about 299 m² /g, and a layer repeat distance of 18.8 Å.

I. Propane and Iso-Butane Dehydrogenation Procedure

A pillared mica sample (1.5 grams) was added to a quartz reactor tube and reduced under flowing H₂ (100 milliliters/minute) at 500° C. for 1 hour at 1 atmosphere. For propane dehydrogenation reactions, the temperature was raised to 605° C. and a mixture of hydrogen and propane at a molar ratio of about 0.3 was passed over the mica sample at 1 atmosphere pressure. The products were constantly monitored using an on-line gas chromatography. Products were reported after 1 hour on stream. For iso-butane dehydrogenation reactions, the temperature was raised to 575° C. and a mixture of hydrogen and isobutane/argon (11 vol. % iso-butane in argon) at a molar ratio of about 3.0 was passed over the mica at 1 atmosphere pressure. Products were reported after 10 hours on stream. This invention is illustrated by the following, non-limiting examples.

EXAMPLE 1 (COMPARATIVE)

A 1.0% Pt by weight pillared mica (Mica A) was prepared as set forth above and washed after calcination. It was tested for propane and iso-butane dehydrogenation. The results are reported in Tables 1 and 2, respectively.

EXAMPLE 2

A 1.0% Pt by weight pillared mica (Mica B) containing 2.5 wt. % Ga was prepared as previously described and tested for propane and iso-butane dehydrogenation. The results are reported in Tables 1 and 2, respectively.

EXAMPLE 3

A 1.0% Pt by weight pillared mica containing 0.4 wt. % Sn (Mica C) was also prepared as set forth above and tested for propane and iso-butane dehydrogenation. The results are reported in Tables 1 and 2, respectively.

                  TABLE 1                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF PROPANE                                                                    Propane   Propylene                                                                              Propane                                        Composition   Conversion                                                                               Selectivity                                                                            Yield                                     Mica (wt. %)       (wt. %)   (wt. %) (wt. %)                                   ______________________________________                                         A    1 Pt--0.4 Na  29        84      24                                        B    2.5 Ga/1 Pt--0.4 Na                                                                          31        96      30                                        C    0.4 Sn/1 Pt--0.4 Na                                                                          36        94      32                                        ______________________________________                                          Reaction Conditions: 605° C.; 1 atmosphere; LHSV = 1; sample time       hour                                                                     

As shown in Table 1, the addition of 2.5 wt. % Ga (Mica B) and 0.4 wt. % Sn (Mica C) to the Pt pillared mica increased propane conversion and enhanced propylene selectivity. The bimetallic micas produce little hydrogenolysis (i.e. C₁ -C₂) or oligomerization (i.e. ≧C₄) products.

                  TABLE 2                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF ISO-BUTANE                                                                           Iso-    Iso-                                                         Iso-Butane                                                                               Butylene                                                                               Butylene                                       Composition   Conversion                                                                               Selectivity                                                                            Yield                                     Mica (wt. %)       (wt. %)   (wt. %) (wt. %)                                   ______________________________________                                         A    1 Pt--0.4 Na  33        71      23                                        B    2.5 Ga/1 Pt--0.4 Na                                                                          46        90      41                                        C    0.4 Sn/1 Pt--0.4 Na                                                                          48        81      39                                        ______________________________________                                          Reaction Conditions: 575° C.; 1 atmosphere; LHSV = 1; sample time       10 hours                                                                 

Table 2 demonstrates that the bimetallic mica catalysts, Pt-Ga (Mica B) and Pt-Sn (Mica C) show increased iso-butane conversions with concomitant increase in iso-butylene selectivities when compared with Mica A which contained only platinum.

EXAMPLE 4 (COMPARATIVE)

A 0.6% Pt by weight pillared mica (Mica D) was prepared and washed after calcination to reduce sodium content. Mica D was tested for iso-butane dehydrogenation. The results are reported in Table 3 below.

EXAMPLE 5

A 0.6% Pt by weight pillared mica (Mica E) containing 2.5 wt. % Ga was prepared. The mica was washed after calcination, providing a Na level of about 0.5% by weight. The mica was tested for iso-butane dehydrogenation, and the results are reported in Table 3 below.

EXAMPLE 6

A 0.6% Pt by weight pillared mica (Mica F) was prepared, containing 0.4 wt. % Sn and tested for iso-butane dehydrogenation. The mica was also washed after calcination, providing an Na level of about 0.5% by weight. The results are reported in Table 3 below.

                  TABLE 3                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF ISO-BUTANE                                                              Iso-Butane                                                                               Iso-Butylene                                                                            Iso-Butylene                                     Composition                                                                               Conversion                                                                               Selectivity                                                                             Yield                                       Mica (wt. %)    (wt. %)   (wt. %)  (wt. %)                                     ______________________________________                                         D    0.6 Pt--0.5 Na                                                                            44        66       29                                          E    2.5 Ga/    39        91       35                                               0.6 Pt--0.5 Na                                                            F    0.4 Sn/    50        87       44                                               0.6 Pt--0.5 Na                                                            ______________________________________                                          Reaction Conditions: 575° C.; 1 atmosphere; LHSV = 1; sample time       10 hours                                                                 

As was observed for the 1% Pt by weight pillared mica, a 0.6% Pt by weight pillared mica also exhibits increased iso-butylene yields and selectivity with the addition of Ga (Mica E) or Sn (Mica F).

EXAMPLE 7

A 0.6% Pt by weight pillared mica (Mica G) was prepared but was not washed after calcination in order to maintain a sodium level of about 1.4% by weight. SnCl₂ (0.4 wt. % Sn) was added via wet impregnation techniques. Mica G was tested for iso-butane dehydrogenation, and the results are reported in Table 4 below.

EXAMPLE 8

A 0.6% Pt by weight pillared mica (Mica H) was prepared but was not washed after calcination in order to maintain a sodium level at about 1.4 wt. %. NaNO₃ (5 wt. % Na) and SnCl₂ (0.4 wt. %) was added via wet impregnation techniques. Mica H was tested for isobutane dehydrogenation, and the results are reported in Table 4 below.

EXAMPLE 9

A 0.6% Pt by weight pillared mica (Mica I) was prepared but was not washed after calcination in order to maintain a sodium level of about 1.4% by weight. Mg(NO₃)₂ (0.5 wt. % Mg) and SnCl₂ (0.4 wt. % Sn) were added via wet impregnation techniques. Mica I was tested for iso-butane dehydrogenation, and the results are reported in Table 4 below.

                  TABLE 4                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF ISO-BUTANE                                                               Iso-Butane                                                                               Iso-Butylene                                                                            Iso-Butylene                                    Composition Conversion                                                                               Selectivity                                                                             Yield                                      Mica (wt. %)     (wt. %)   (wt. %)  (wt. %)                                    ______________________________________                                         F    0.4 Sn/     50        87       44                                              0.6 Pt--0.5 Na                                                            G    0.4 Sn/     53        92       48                                              0.6 Pt--1.4 Na                                                            H    5 Na--0.4 Sn/                                                                              27        94       26                                              0.6 Pt--1.4 Na                                                            I    0.5 Mg--0.4 Sn/                                                                            60        94       57                                              0.6 Pt--1.4 Na                                                            ______________________________________                                          Reaction Conditions: 575° C.; 1 atmosphere; LHSV = 1; sample time       10 hours                                                                 

The above table shows that Pt-pillared micas which are not washed after the calcination step to maintain native sodium levels exhibit higher iso-butane conversions and iso-butylene selectivities (Mica G). However, excess amounts of sodium (>5 wt. %), while maintaining iso-butylene selectivity, decreases iso-butane conversion and iso-butylene yield (Mica H). The addition of an alkaline earth modifier further maximizes iso-butylene yields (Mica I compared to Mica G).

Table 5 below compares the performance of Mica I when used with a hydrogen co-feed, without a hydrogen co-feed, an at higher feed space velocities.

                  TABLE 5                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF ISO-BUTANE                                                               Iso-Butane                                                                               Iso-Butylene                                                                            Iso-Butylene                                    Composition Conversion                                                                               Selectivity                                                                             Yield                                      Mica (wt. %)     (wt. %)   (wt. %)  (wt. %)                                    ______________________________________                                         .sup. I                                                                             0.5 Mg--0.4 Sn/                                                                            60        94       57                                              0.6 Pt--1.4 Na                                                            .sup.1 I                                                                            0.5 Mg--0.4 Sn/                                                                            59        95       57                                              0.6 Pt--1.4 Na                                                            .sup.2 I                                                                            0.5 Mg--0.4 Sn/                                                                            47        96       45                                              0.6 Pt--1.4 Na                                                            ______________________________________                                          Reaction Conditions: 575° C.; 1 atmosphere; LHSV = 1; sample time       10 hours.                                                                      .sup.1 H.sub.2 /iC4 = 0. .sup.2 LHSV = 3.                                

As shown in the above table, an alkaline modified Pt-Sn pillared mica exhibits similar iso-butylene yields without a hydrogen co-feed (catalyst ¹ I). At higher feed space velocities, lower iso-butylene yields are produced (catalyst ² I).

EXAMPLE 10

A 0.6% Pt by weight pillared mica (Mica J) was prepared but was not washed in order to maintain a sodium level at about 1.4% by weight. Mg(NO₃)₂ (0.1 wt. % Mg) and SnCl₂ (0.4 wt. % Sn) were added via wet impregnation techniques. Mica J was tested for iso-butane dehydrogenation, and the results are reported in Table 6 below.

EXAMPLE 11

A 0.6% Pt by weight pillared mica (Mica K) was prepared but was not washed in order to maintain a sodium level at about 1.4% by weight. Mg(NO₃)₂ (1 wt. % Mg) and SnCl₂ (0.4 wt. % Sn) were added via wet impregnation techniques. Mica K was tested for iso-butane dehydrogenation, and the results are reported in Table 6 below.

                  TABLE 6                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF ISO-BUTANE                                                               Iso-Butane                                                                               Iso-Butylene                                                                            Iso-Butylene                                    Composition Conversion                                                                               Selectivity                                                                             Yield                                      Mica (wt. %)     (wt. %)   (wt. %)  (wt. %)                                    ______________________________________                                         I    0.5 Mg--0.4 Sn/                                                                            60        94       57                                              0.6 Pt--1.4 Na                                                            J    0.1 Mg--0.4 Sn/                                                                            50        86       43                                              0.6 Pt--1.4 Na                                                            K    1 Mg--0.4 Sn/                                                                              40        95       38                                              0.6 Pt--1.4 Na                                                            ______________________________________                                          Reaction Conditions: 575° C.; 1 atmosphere; LHSV = 1; sample time       10 hours                                                                 

The above table shows that iso-butylene yields are maximized with a 0.5 wt. % Mg modifier (Mica I). Lower (Mica J) or higher (Mica K) Mg loadings decrease iso-butylene yields.

EXAMPLE 12

A 0.6% Pt by weight pillared mica (Mica L) was prepared but was not washed in order to maintain a sodium level at about 1.4% by weight. NaOH (0.5% Na) and SnCl₂ (0.4% Sn) were added via wet impregnation techniques. Mica L was tested for iso-butane dehydrogenation, and the results are reported in Table 7 below.

EXAMPLE 13

A 0.6% Pt by weight pillared mica (Mica M) was prepared but was not washed in order to maintain a sodium level at about 1.4 wt. %. Ca(NO₃)₂ (0.5 wt. % Ca) and SnCl₂ (0.4 wt. % Sn) were added via wet impregnation techniques. Mica M was tested for iso-butane dehydrogenation, and the results are reported in Table 7 below.

EXAMPLE 14

A 0.6% Pt by weight pillared mica (Mica N) was prepared but was not washed in order to maintain a sodium level at about 1.4 wt. % Nd(NO₃)₃ (0.5 wt. % Nd) and SnCl₂ (0.4 wt. % Sn) were added via wet impregnation techniques. Mica N was tested for isobutane dehydrogenation, and the results are reported in Table 7 below.

                  TABLE 7                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF ISO-BUTANE                                                               Iso-Butane                                                                               Iso-Butylene                                                                            Iso-Butylene                                    Composition Conversion                                                                               Selectivity                                                                             Yield                                      Mica (wt. %)     (wt. %)   (wt. %)  (wt. %)                                    ______________________________________                                         I    0.5 Mg--0.4 Sn/                                                                            60        94       57                                              0.6 Pt--1.2 Na                                                            L    0.5 Na--0.4 Sn/                                                                            54        94       51                                              0.6 Pt--1.2 Na                                                            M    0.5 Ca--0.4 Sn/                                                                            38        95       36                                              0.6 Pt--1.2 Na                                                            N    0.5 Nd--0.4 Sn/                                                                            35        93       33                                              0.6 Pt--1.2 Na                                                            ______________________________________                                          Reaction Conditions: 575° C.; 1 atmosphere; LHSV = 1; sample time       10 hours.                                                                

The above table shows that magnesium and sodium modifiers (Mica I and L) produce greater iso-butylene yields compared to either a calcium (Mica M) or a neodymium (Mica N) modifier. High iso-butylene selectivities (>93%) are maintained in all cases.

EXAMPLE 15

A 0.6% Pt-0.5% Nd pillared mica (Mica O) was prepared from a Nd-CHLORHYDROL solution as set forth above but was not washed in order to maintain a sodium level at about 1.4 wt. %. SnCl₂ (0.4 wt. % Sn) was added via wet impregnation techniques. Mica O, the resulting mica, was tested for iso-butane dehydrogenation, and the results are reported in Table 8 below.

                  TABLE 8                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF ISO-BUTANE                                                               Iso-Butane                                                                               Iso-Butylene                                                                            Iso-Butylene                                    Composition Conversion                                                                               Selectivity                                                                             Yield                                      Mica (wt. %)     (wt. %)   (wt. %)  (wt. %)                                    ______________________________________                                         N    0.5 Nd--0.4 Sn/                                                                            35        93       33                                              0.6 Pt--1.2 Na                                                            O    0.4 Sn/0.5 Nd--                                                                            58        91       53                                              0.6 Pt--1.2 Na                                                            ______________________________________                                          Reaction Conditions: 575° C.; 1 atmosphere; LHSV = 1; sample time       10 hours.                                                                

The above table shows that iso-butylene yields are maximized when the rare earth modifier is added with the Pt-CHLORHYDROL solution prior to the pillaring step (Mica O) rather than added to the pillared mica via wet impregnation techniques (Mica N).

EXAMPLE 16 (COMPARATIVE)

A 0.6% Pt by weight pillared bentonite clay (Clay 1) was prepared as set forth above and was tested for iso-butane dehydrogenation. The results are reported in Table 9 below.

EXAMPLE 17 (COMPARATIVE)

SnCl₂ (0.4 wt. % Sn) was added to a 0.6% Pt by weight pillared bentonite clay via wet impregnation techniques. The resulting clay (Clay 2) was tested for iso-butane dehydrogenation, and the results are reported in Table 9 below.

EXAMPLE 18 (COMPARATIVE)

NaNO₃ (1.2 wt. % Na) and SnCl₂ (0.4 wt. % Sn) were added to a 0.6% Pt by weight pillared bentonite clay via wet impregnation techniques. The resulting clay (Clay 3) was tested for iso-butane dehydrogenation. The results are reported in Table 9 below.

                  TABLE 9                                                          ______________________________________                                         RELATIVE PERFORMANCE OF MICAS                                                  FOR DEHYDROGENATION OF ISO-BUTANE                                                                Iso-Butane                                                                               Iso-Butylene                                                                            Iso-Butane                                      Composition Conversion                                                                               Selectivity                                                                             Yield                                     Mica  (wt. %)     (wt. %)   (wt. %)  (wt. %)                                   ______________________________________                                         O     0.6 Pt--0.5 Na                                                                             44        66       29                                        Clay 1                                                                               0.6 Pt--0.1 Na                                                                             11        82       9                                         Clay 2                                                                               0.4 Sn/                                                                        0.6 Pt--0.1 Na                                                                              6        83       5                                         Clay 3                                                                               1.4 Na--0.4 Sn/                                                                             2        82       1                                               0.6 Pt--0.1 Na                                                           G     0.4 Sn/     53        92       48                                              0.6 Pt--1.4 Na                                                           ______________________________________                                          Reaction Conditions: 575° C.; 1 atmosphere; LHSV = 1; sample time       10 hours.                                                                

The above table shows that a Pt-pillared clay bentonite (Clay 1) is lower in dehydrogenation activity than a similar Pt-pillared mica (Mica O). Upon addition of Sn (Clay 2) or Sn and Na modifiers (Clay 3) a further reduction in activity is observed. This behavior is contrasted with the modified Pt-pillared mica (Mica G) which showed dehydrogenation activity and selectivity credits upon modification.

II. Regeneration of Dehydrogenation Micas Which Had Been Used as catalysts

EXAMPLE 19

Regeneration for a 0.5 Mg-0.4 Sn/0.6 Pt-1.4 Na pillared mica (Mica I) employed a flow of air (100 milliliters/minute) for 2 hours at 550° C. Following a N₂ purge, the mica was reduced under a flow of H₂ (100 milliliters/minute) for 1 hour at 500° C. The dehydrogenation of iso-butane was carried out as described in earlier examples. The iso-butylene yield with two regeneration sequences after about 6, 10, 15 days on feed was obtained.

During the first yield period lasting 6.5 days, iso-butylene yields ranged from 53 to 40 wt. %. After a regeneration sequence described above, the second yield period lasting 3.75 days produced iso-butylene yields ranging from 51 to 43 wt. %. Following catalyst regeneration a third yield period lasting 4.5 days gave iso-butylene yields ranging from 52 to 43 wt. %. This example evidences the fact that the mica catalysts of the present invention can withstand a series of regenerations without a decrease in dehydrogenation activity. 

What is claimed is:
 1. A pillared mica comprising an active metal selected from the group consisting of Pt, Cr, Pd, Ir, Rh and mixtures thereof and a modifier metal selected from the group consisting of Sn, ga and mixtures thereof, wherein the height of said pillars is about 5 to 20Å.
 2. The pillared mica of claim 1, wherein said mica is a tetrasilicic mica.
 3. The pillared mica of claim 1, which is further modified with a second metal selected from the group consisting of alkali metals, alkaline earth metals or rare earth metals and mixtures thereof.
 4. The pillared mica of claim 1 wherein said pillar is substantially comprised of a metal oxide selected from the group consisting of alumina, zirconia, chromia or mixtures thereof.
 5. The pillared mica of claim 4 wherein said pillar is comprised of alumina.
 6. The pillared mica of claim 1, which contains from about 0.05 to 2 wt. % of an active metal or mixture of active metals.
 7. The pillared mica of claim 6, which contains from about 0.1 to 1.5 wt. % of an active metal or mixture of active metals.
 8. The pillared mica of claim 1, which contains from about 0.05 to 5 wt. % of a mixture of Sn and Ga.
 9. The pillared mica of claim 1, wherein said pillared mica comprises from about 0.1 to 1 wt. % Sn and Ga is substantially absent.
 10. The pillared mica of claim 1, wherein said pillared mica comprises from about 0.1 to 3 wt. % Ga and Sn is substantially absent.
 11. The pillared mica of claim 1 wherein said pillared mica comprises from about 0.1 to 2 wt. % of a second modifier metal selected from the group consisting of alkali, alkaline or rare earth elements.
 12. The pillared mica of claim 5 wherein said pillared mica comprises from about 0.1 to 2 wt. % of a second modifier metal selected from the group consisting of alkali, alkaline or rare earth elements.
 13. The pillared mica of claim 11 wherein said second modifier metal is selected from the group consisting of Na, Mg, Ca, Nd, La and Ce.
 14. A process for the preparation of a pillared mica, said process comprising the following steps:(a) treating a mica with an aqueous polymeric cationic hydroxy multimetal complex solution comprising: (i) a polymeric cationic hydroxy complex solution, wherein the cation is selected from the group consisting of aluminum, zirconium, chromium or mixtures thereof, and (ii) 0.05 to 2 wt. % of an active metal compound wherein the metal is selected from the group consisting of Pt, Cr, Pd, It, Rh and mixtures thereof; (b) calcining said treated mica for an effective amount of time at an effective temperature, thereby forming metal oxide pillars between the mica layers; (c) incorporating from 0.05 to 5 wt. % of a modifier metal selected from the group consisting of Sn, Ga and mixtures thereof.
 15. The process of claim 14 wherein all of the metals are incorporated into said mica by an incipient wetness method.
 16. The process of claim 14, wherein about 0.1 to 2 st. % of a second modifier metal is used which is selected from the group consisting of alkali metals, alkaline earth metals, rare earth elements.
 17. The process of claim 16 wherein an active metal selected from the group consisting of Pt, Cr, Pd, Rh or a mixture thereof is present in a range from about 0.1 to 1.5 wt. %; and about 0.1 to 1 wt. % of said second modifier metal is present; and the cation of the polymeric cationic hydroxy complex solution is aluminum. 